Electrical igniter cap

ABSTRACT

An electrical igniter cap has a reproducible igniter characteristic by virtue of the fact that, at the firing side, an igniter unit  20  is covered by a foil of plastic material, which is rupture-resistant but tears quickly, and also at the firing side it bears against a sieve plate  28  with defined hole cross-sections.

[0001] The invention relates to an electrical igniter cap as set forth in the classifying portion of claim 1.

[0002] In accordance with an unpublished data specification sheet an electrical igniter cap comprises a housing which, besides the electrical firing device, contains two igniter charges and a bursting or explosion charge. Those igniter caps involve major fluctuations in terms of firing power and performance. Because of an excessively rapid pressure rise and an excessively high gas pressure peak, a large number of cartridge case failures occurred. The igniter unit does not have any cover member so that loosening thereof occurred when drop tests were carried out. Drop tests therefore resulted in the igniter cap being fired.

[0003] The object of the invention is to propose an electrical igniter cap which reliably ignites propellent charge powder, which affords a uniform output performance and which is safe.

[0004] That object is attained by the invention in accordance with the characterising features of claim 1. Advantageous developments of the invention are to be found in the appendant claims.

[0005] In accordance with the invention, no faults occur in the igniter cap after an environmental test such as a jolt test and drop tests. No gap or crack formation occurs, which could result in premature firing. The firing output performance is reproducible. The gas pressure curve is in a range which ensures reliable ignition of the bursting charge comprising propellent charge powder.

[0006] Essential aspects in this respect are the sieve or screening plate with sufficiently large gas openings and the plastic foil which is resistant to rupture but which tears quickly. The plastic foil therefore tears in a defined manner in the cross-sections of the gas openings.

[0007] In accordance with claim 2, the sieve plate bears with a predetermined pressing force against the plastic foil and causes the igniter unit or composition to bear firmly against the electrical firing device. No crack or gap formation can therefore occur in the region of the igniter unit.

[0008] In accordance with claim 3, the arrangement has sufficiently large hole cross-sections for the gases of the igniter unit.

[0009] The firing wire bridge embedded in the igniter unit, as set forth in claim 4, ensures reliable ignition of the igniter unit. It is enclosed except for the pole surface by the igniter unit. That means that the arrangement affords a large igniter surface area.

[0010] In accordance with claim 5 the plastic foil comprises HDPE (high density polyethylene). It can also comprise another suitable plastic material.

[0011] An embodiment of the invention is described hereinafter and illustrated in the drawing.

[0012] An electrical igniter cap 1 comprises a housing 2 which has openings 4, 5 closed by lacquer 3, at both ends.

[0013] Supported in a receiving bore 10 are an electrical firing device 11 with pole bodies 12, 13 and an insulating ring 14 disposed therebetween. An eccentrically disposed firing wire bridge 15 is soldered to the pole bodies 12, 13 in known manner.

[0014] An igniter composition or unit 20 is pressed on to the electrical firing device 11 and encases the firing wire bridge 15.

[0015] The igniter unit 20 is covered by a plastic foil 21 which is resistant to rupture but which tears quickly, comprising high density polyethylene (HDPE).

[0016] A cup 25 is pressed into the receiving bore 10 and contains a bursting or explosion charge 26. The cup 25 is in the form of a sieve plate 28 at its bottom. The cross-sections of the gas flow openings 29 amount to 50% of the cross-section (not shown) of the receiving bore 10.

[0017] A flanged edge 32 fixes a ring 33 and a disc 34. That provides that the cup 25 is fixed in position and, by way of the sieve plate 28, presses the foil 21 and the igniter unit 20 against the pole bodies 12, 13, with a certain biasing force.

[0018] Jolt tests and drop tests therefore do not have any influence on the strength and firmness of the igniter unit 20.

[0019] Upon firing of the igniter unit 20, at a certain gas pressure the foil portions disposed in the region of the gas flow openings 29 abruptly tear and the bursting charge 26 is ignited over a large area. The gas pressure of the bursting charge 26 destroys the disc 34 and the lacquer 3.

[0020] The igniter cap 1 has a comparatively large bursting charge 26, more specifically being of the same structural length as the known igniter cap. That is achieved primarily by a saving of space insofar as the igniter cap 1 according to the invention has only one single igniter unit 20.

[0021] The functions of the foil 21 are to hold the igniter unit 20 and to provide for substantially uniform ignition of the igniter unit 20. The firing wire bridge 15 fires asymmetrically. Due to the retarding, damming action of the foil 21, the igniter unit 20 is fired therethrough, over its entire cross-section. Ignition of the bursting charge 26 therefore takes place through all gas flow openings 29 and not just through a part thereof. The foil 21 can also comprise plastic material or metal such as copper, aluminium, or a suitable composite material. 

1. An electrical igniter cap (1) comprising a housing (2), a bursting charge (26), an igniter unit (20) and an electrical firing device (12-15), characterised in that arranged between the bursting charge (26) and the igniter unit (20) is a sieve plate (28) with a foil (21) of plastic material, which foil is rupture-resistant but tears quickly.
 2. An igniter cap according to claim 1 characterised in that the sieve plate (28) is a part of a cup (25), and the cup (25) surrounds the bursting charge (26) and is secured by fixing portions (33, 34) which are flanged in place.
 3. An igniter cap according to claim 2 characterised in that the cross-sections of the openings of the sieve plate are 30-70% of the cross-section of the receiving bore (10).
 4. An igniter cap according to claim 1 characterised in that a firing wire bridge (15) is embedded in the igniter unit (20).
 5. An igniter cap according to claim 1 characterised in that the plastic foil comprises high density polyethylene (HDPE) or another suitable plastic material or metal or a suitable composite material. 